Burkhard Wilske, Nan Lu, Ranjeet John and Jiquan Chen (Univ. of Toledo)

1. Lessons learned from “Effects of Land Use Change (LUC) on the Energy and Water Balance of the Semi-Arid Region of Inner Mongolia, China” [NEWS 2004 NRA: NN-H-04-Z-YS-005-N]: NNG06GA70G Burkhard Wilske, Nan Lu, Ranjeet John and Jiquan Chen(Univ. of Toledo) Project PIs & Collaborators: Asko Noormets, Steve McNulty, Ge Sun (USDA Southern Global Change Program), Guanghui Lin, Yanfen Wang (Inst. of Botany - Chinese Acad. of Sciences, IBCAS), Xiangming Xiao (Univ. of New Hampshire), Jiaguo Qi (MI State Univ.), Dennis Ojima, Scott Denning (Colorado State Univ.), Ke Guo, Jian Ni, Xingguo Han, Osbert Sun, and Linhao Li (IBCAS) Introduction Inner Mongolia (IM, Autonomous Region) in northern China has a population of ~25 million and covers an area of 1.18 million km² (i.e., the area of Texas plus California). IM is composed of 41% grassland, 10% shrubland, 24% desert, 8% forest and 13% cropland (Fig. 1). Semi-arid grasslands were considered as IM’s most important renewable resource; however, land use change (LUC) and land degradation/desertification threaten this resource and thereby the overall water and energy balance of the area. The main features of LUC in IM include local overgrazing due to a reduction in nomadic lifestyle, land cultivation and irrigation for agriculture, and forestation to protect human efforts from deserti-fication. Our joint research set out to address the biophysical basis of these problems. Eddy-covariance (EC) measurements at eight exemplary sites have delivered water, carbon and energy fluxes since the end of 2004. In addition to evaluating site-to-site changes, the obtained ground data was correlated with remote sensing products to model and display feedbacks from LUC and water/energy balance on a regional scale. Sites: Dongwu Xilinhot XD, XF Duolun DC, DS Kubuqi K04, K05 (Daxing) Fig.1 Cardinal Results LUC – Water balance • Cultivation of grasslands decreased ecosystem evapotranspiration (ET) by 15% and 7% during wet and dry years, respectively. Grazing decreased ET by 13% and 0% during wet and dry years, respectively (Fig. 2). Reduction in annual ET under both regimes was apparently associated with changes in canopy surface conductance, soil water holding capacity and reduced soil moisture. • Decreased ET/PET (Potential ET) ratios suggest less drought stress of the vegetation in the affected areas. The human-induced changes in ET seemingly relaxed the water balance, which is in contradiction to observed desertification processes with increased grazing and cultivation. • Large-scale plantations of poplar trees, established to combat desertification, increased ET as compared with natural shrubland (i.e., the vegetation cover developing under lower water availability than required for a grassland) (Fig. 3). • Increased ET with poplars in semi-arid IM is only possible through irrigation or with trees tapping groundwater. We calculated that large plantations along the Yellow River will consume a water volume equivalent to 6.5 - 15% of its mean stream flow. Thus, growth of extensive plan-tations can significantly reduce groundwater levels and increase drought stress in the area (Fig. 4). Fig.4 Increased water discharge with poplar plantations growing on former semiarid shrub land. In our example, ET of a natural shrub land has no signi-ficant effect (upper panel) on water discharge in the area. A 6-yr year old poplar plantation (mid panel) and one close to crown closure (lower panel) will discharge water equivalent to 6.5% and 15% of the Yellow River mean stream (www.yellowriver.gov.cn). Fig. 2 Changes in monthly ET and mean ET/PET ratio during wet (2006) and dry (2007) growing seasons between steppe (DS) and cultivated steppe (DC, cropland), and fenced steppe (XF) and heavily grazed steppe (XD, degraded) in Inner Mongolia. Fig. 3 Correlation between ET from poplar plantation (K04) and shrub land (K05)(growing season 2006): Non-gap-filled isochronal 30-min averages screened for stepwise focused parameter similarity between sites : Linear regressions (a)-(c) difference in T<1°C, (a) differences in soil moisture □=19-22% and Δ=17% Symbols ■, ▲restrict further “Rn<1 Wm-2”. Regressions (b=■) and (c=▲) were further filtered for differences in u <1 ms-1, VPD<1%, and during daytime only. Main outputs LUC – Energy balance 1 http://research.eeescience.utoledo.edu/lees/_H2O&Energy Miao H, Chen S., Chen J, Zhang W, Zhang P, Wei L, Lin G. Cultivation and grazing altered ET and dynamics in Inner Mongolia steppes. Agricultural and Forest Meteorology, in press. Wilske B, Lu N, Wei L, Chen S, Zha T, Liu C, Xu W, Noormets A, Huang J, Wei Y, Chen J, Zhang Z, Ni J, Sun G, Guo K, McNulty S, John R, Chen J, Han X, Lin G. Poplar plantation has the potential to alter water balance in semiarid Inner Mongolia. Agricultural and Forest Meteorology, submitted 10/14/2007. Chen S,Chen J, Lin G, Zhang W, Miao H, Wei L, Huang J, Han X. Energy balance and partition in Inner Mongolia steppe ecosystems with different land use types. Agricultural and Forest Meteorology, accepted. Shao S, Chen J, Li L, Xu W, Chen S, Tenney G, Xu J, Zhang W. How do spatial variations of net radiation and soil heat flux contribute to energy enclosure at flux measurement sites. Agricultural and Forest Meteorology, accepted. Zhang WL, Chen SP, Chen J, Wei L, Han XG, Lin GH. 2007. Bio-physical regulations of carbon fluxes of a steppe and a cultivated cropland in semiarid Inner Mongolia. Agricultural and Forest Meteorology 146: 216-229. Lu N, John R, Wilske B, Ni J, Chen J. Impact of land cover and vegetation heterogeneity on spatial variability of surface soil moisture in a semiaird region. Agricultural and Forest Meteorology, (submitted). John R, Chen J, Lu N, Guo K, Liang C, Wei Y, Noormets A, Ma K, Han X. 2008. Predicting plant diversity based on remote sensing products in the semi-arid region of Inner Mongolia. Remote Sensing of Environment 112: 2018-2032. 2 • Seasonal changes in net radiation (Rn), Latent heat (LE), sensible heat (H) and soil heat (G) at cultivated, overgrazed and control sites (natural steppe) were similar in showing very low values during the snow cover from December to February and increasing trends in the growing season. • Large decreases in stomatal conductance (gc) obviously limited the LE partitioning of available energy (Rn-G) in these semi-arid ecosystems and hence human-disturbed sites showed a decreased LE fraction within a shorter phenological period (Fig. 5). • Reductions in gc and the decoupling factor (Ω) in the cropland as well as the degraded steppe suggested that LUC could depress latent flux fraction and increase its sensitivity to air and soil drought. • Spatial variability of the energy balance ε as obtained from eight plots was as high as 40 Wm-2 by a daily mean (Fig. 6). Particularly for heterogeneous and/or overgrazed steppe, there still exists an urgent need to improve the energy balance closure. 3 4 5 6 7 Fig. 5 Seasonal patterns of 5-day averages of midday mean LE/LEeq, Bowen ratio (β), canopy conductance (gc) and decoupling coefficient (Ω) of four sites in Inner Mongolia, from 1 Dec 2005 to 31 Nov 2006. Midday means include 10:00 - 15:00 h local standard time. Fig. 6 Spatial variability of Rn and soil heat flux (G+S) contribute to energy enclosure at steppe sites in IM: Upper and lower bound of the gray band represent (Rnmax–(G=S)min) and (Rnmin–(G=S)max), respectively (of 8 plots). 8 see also posters NASA Carbon Cycle and Ecosystems Joint Science Workshop, Adelphi, MD, April 28 – May 2, 2008 #262 N. Lu et al., #295 R. John et al.